1. Field of Invention
The present invention relates to a traveling device, more particularly a device for traveling easily on an uneven ground or an inclined surface.
2. Description of Related Art
Among the traveling devices, a hand-operated device such as a wheelchair usually does not have a suspension, so that it is difficult to advance on uneven ground smoothly. In a case of an electric-powered wheelchair, it is well-known art to use a spring type suspension for contacting its driving wheel to the ground effectively. In this case, however, since it is difficult to extend the stroke of the spring, its function is limited and the wheelchair is not able to ride over acutely uneven ground. Moreover, no matter whether it is hand-operated or electric-powered, an usual wheelchair has a pair of driving wheels as rear wheels and a pair of casters as front wheels, while its gravity center is located between the rear and front wheels. This means that it is difficult for the wheelchair to run straight on an one-way sloping ground, since it causes a moment for turning the body of the wheelchair downwardly.
For solving such problem, Japanese patent laid-open No. 52 (1977)-77342 proposes an electric-powered wheelchair having four driven wheels which are adapted to turn by means of power-steering. However, the structure of the wheelchair is complex and expensive. Moreover, when one of the wheels strikes and mounts a projection on the ground, the weight of the wheelchair is imposed on only the mounting wheel and the diagonally opposite wheel, such that the other two wheels are lifted up so as to reduce the stability of the wheelchair.
Japanese patent laid-open No. 10 (1998)-85261 discloses a wheelchair having a pair of left and right lower frames extending from the front to the back and supporting a pair of front wheels and a pair of rear wheels, and an upper frame for supporting a seat. Both upper and lower frames curve downwardly between the front and rear wheels. This wheelchair is adapted to improve the grounding ability of the wheels by the flexion of the frame. However, this wheelchair is not suitable enough on acutely uneven ground, similar to the one using the spring suspension.
The primary object of the present invention is to provide a traveling device such as a hand-operated or electric-powered wheelchair having each wheel which moves along and in conformity with an uneven ground so as to allow a comfortable driving thereon, structure of which is simple and able to manufacture at low price.
To achieve this object, a traveling device according to the present invention comprises:
a truck member acting as a platform and having a loop frame, and a pair of front and rear casters and a pair of left and right driving wheels for supporting the loop frame,
said loop frame consisting of a pair of side frame parts and a pair of front and rear frame parts, each side frame part having a front section and a rear section divided by a bendable portion at which the side frame part is able to bend upwards and downwards, said bendable portions being formed at a pair of opposed lengthwise middle portions of the side frame parts,
said pair of casters supporting a pair of lengthways middle portions of the front and rear frame parts,
said pair of driving wheels supporting the pair of opposed lengthwise middle portions of the side frame parts, and allowing the truck member to move frontwards and backwards;
and a body member having a front body portion which is supported by a pair of links, and a rear body portion which is supported by a pair of fixed arms,
said each link having an upper end and a lower end, the lower end of each said link being connected to the front section of the side frame part,
while said each fixed arm having a lower end and an upper end, the lower end of each said fixed arm being connected to the rear section of the side frame part,
wherein the upper and lower ends of the each link is rotatably connected so as to move generally parallel to a traveling direction into which the driving wheel is heading, whereby the upper end of the each fixed arm is fixed immovably, while the lower end of the each fixed arm is rotatably connected so as to move generally parallel to the traveling direction.
The secondary object of the present invention is to prevent the traveling device from being unstable due to excessive bending of the loop frame. To achieve this object, the traveling device is provided with a stopper for regulating the bending of the loop frame.
The third object of the present invention is to further improve the stability of the traveling device, particularly reducing the risk of it turning over obliquely with respect to the direction of travel. This object is achieved by providing a pair of auxiliary wheels on the both sides of the caster.
The fourth object of the present invention is to provide a traveling device with casters which are able to ride over the projection in the uneven ground with ease. To achieve this object, the present invention proposes a traveling device in which each bendable portion is located beneath (or lower than) a rotation axis of the driving wheel, or a traveling device in which each bendable portion is located beneath the rotation axis of the driving wheel and as high as a rotation center of the front caster.
The fifth object of the present invention is to further reduce the risk of the traveling device turning over obliquely with respect to the direction of travel. For this purpose, the traveling device further comprises an oscillation arm which is turnably (or rotationally) supported by a pivot axis protruding from a center of the front or rear frame part, wherein at least either of the front and rear casters is formed into a pair of casters provided at both sides of the oscillation arm.
The sixth object of the present invention is to construct the traveling device compactly by inserting a generally flat truck member below a body member as a carrier. For this purpose, the loop frame is formed into a generally horizontal form as seen from left and right sides.